In effecting a fluid seal between a large rectangular hydraulic ram vertically movable with respect to a stationary fluid reservoir, a lip-type seal is customarily used. However, lip-type seals have a relatively short service life and usually fail after about 10,000 cycles, thus necessitating replacement. Additionally, these seals are molded in one piece and, due to the size of the ram, approximately 8 .times. 28 feet, such molded seals are impractical and unwieldy.
It would be desirable to employ an O-ring type seal; however, commercially available seals require that the clearance between the ram and the pressure vessel not exceed a maximum of 0.016 inches at 400 psi, for example, a 65 durometer rubber O-ring. Moreover, in such large hydraulic rams, the gap that must be sealed between the ram and the pressure vessel generally varies from about 0.190 inches to 0.380 inches or greater, which is well beyond the maximum tolerance that can be effectively bridged and sealed by a conventional O-ring seal.